Portable hand-held working machines powered by internal combustion engines are known since long. These machines are often used for cutting concrete and similar materials. Such a cutting creates a lot of abrasive particulate matter. Also, before introducing the air for combustion in the engine, if the air is not cleaned then the engine may wear out, due to an abrasive action of the particulate matter. Typically, efficient air cleaning is vital and is attained mainly through a filter assembly having a sufficient filter volume, which may increase a service life of the machine.
To achieve an enhanced air cleaning, a centrifugal air cleaning step is typically included before air enters the filter assembly. For example U.S. Pat. No. 7,520,276 and WO 2006/006894 both assigned to Husqvarna AB describe a filter assembly for a portable hand-held working machine. The disclosure of both are herewith incorporated in the present application by reference. The filter assembly utilizes a pre-filter followed by a main filter for further cleaning of centrifugally cleaned air from a fan assembly. The pre-filter is a washable filter while the main filter is a disposable paper filter. This is a fairly efficient, however a rather complicated air cleaning system with two filters and a need for washing the washable filter at certain time intervals. This kind of service is costly. Also the air filter needs to be changed at time intervals.
In light of the foregoing, there is a need for an efficient air cleaning system, for an internal combustion engine of a portable working machine which may have a simple design and a lower number of components and allow longer service intervals.